1. Field of the Invention
The present invention relates to a magnetic head and method for reading and writing information on magnetic media and more particularly to a head having one magnetic core that can read and write very high track density (greater than 1000 TPI) floppy disks and one magnetic core that can read and write conventional track density (less than approximately 135 TPI) floppy disks.
2. Description of the Prior Art
The track density of magnetic storage disks for conventional floppy disk drives is approximately in the range of forty-eight to one hundred thirty-five tracks per inch (TPI). In contrast, optical disk drives are capable of achieving track densities in excess of 15,000 TPI. The higher track densities of optical disk drives are achieved through the use of closed loop optical servos that allow the read/write head to follow data track eccentricities caused by defects in the medium and by disturbances from outside forces. It is well known that the term floppy disk refers to a single disk (i.e. single platter) flexible recording medium.
In rigid type magnetic disk drives, track densities of up to 2100 TPI are presently used. These drives commonly have multiple disks in which both sides are used for data. To achieve the high track density a dedicated surface of one of the disks is used for magnetic track servo information. This surface is then not usable for data storage. Thus, the total capacity of the drive is lessened. The tracking servo information is also capable of being accidentally erased causing loss of access to all data.
Various techniques have been reported for using optical means for acquiring track following servo information contained on a magnetic recording medium. For example, Ahn, et al., in U.S. Pat. No. 4,633,451, issued on Dec. 30, 1986 for "Optical Servo For Magnetic Disks", discloses the use of a laser diode to read track following servo information in the form of a plurality of spots contained in an optical layer positioned above a magnetic recording layer. Ahn, et al. also discloses the positioning of two transducers on a slider. In FIG. 4 of the '451 patent, a magnetic recording transducer is shown positioned on one rail of the slider and an optical transducer is shown positioned on the opposite rail.
N. Koshino and S. Ogawa, in "Optical Method of the Head Positioning in Magnetic Disk Systems", preprint from IEEE Transactions on Magnetics (1980), discloses an apparatus for achieving optical servo control in a magnetic disk system which comprises an LED light source and three optical fibers for delivering light to a medium. The three optical fibers are embedded in a hole in the central rail of a Winchester-type ferrite head. The medium comprises a plurality of circular optical tracks, dyed black, and located underneath a magnetic film.
Neither of these references discloses a magnetic head that can be used with both high track density magnetic media and with conventional floppy disks.